In many applications, one or more low-cost, simple to use, isolated power supplies working from input voltages up to 100V are needed. Some conventional solutions use an isolated buck converter, also known as a flybuck converter, to generate this bias supply. A flybuck converter uses a conventional synchronous buck converter with coupled inductor windings to create isolated outputs. The coupled inductor windings may be implemented by a relatively small transformer for power transfer. The ratio of the primary and secondary turns (see N1 and N2, respectively, in FIG. 1) is well matched, so the secondary output closely tracks the primary output voltage.
As is known in the art and shown in FIG. 1, a flybuck converter is created by replacing the output filter inductor of a synchronous buck converter with a coupled inductor X1 or flyback-type transformer, and rectifying the secondary winding (N2) voltage using a diode D1 and a capacitor COUT2. The capacitor COUT1 and the switches Q1 and Q2 can be the same as used in a synchronous buck converter. The topology of FIG. 1 can be extended to any number of isolated secondary outputs like VOUT2. It also can be used to generate one or more inverting outputs.
As in all power supply scenarios, overcurrent protection and recovery are important features. It is therefore desirable to provide for effective overcurrent recovery in a flybuck converter such as shown in the example of FIG. 1.